1. Field of the Invention
The present invention relates to a piston pump for use in, for example, a vehicular brake apparatus.
2. Description of the Related Art
Piston pumps of such a type are disclosed in, for example, Japanese kohyo (PCT) patent publication No. 2002-514712 (which discloses an ordinary piston pump not having a function of charging fluid into a pump chamber) and Japanese Patent No. 3278982 (which discloses a self-priming piston pump having a function of charging fluid into a pump chamber).
The ordinary piston pump (non-self-priming piston pump) disclosed in Japanese kohyo (PCT) patent publication No. 2002-514712 includes a pump housing having a suction port, a discharge port, and an internal cavity; a first cylinder member having a cylinder bore and built into the internal cavity of the pump housing; a piston built into the cylinder bore of the first cylinder member to thereby form a pump chamber in the cylinder bore and adapted to change the volume of the pump chamber by means of axially reciprocating movement thereof; a suction valve provided in the piston, which opens when the volume of the pump chamber increases, and closes when the volume decreases; and a discharge valve provided at the discharge side of the pump chamber, which opens when the volume of the pump chamber decreases, and closes when the volume increases. The piston axially reciprocates to thereby increase and decrease the volume of the pump chamber, whereby fluid flows from the suction port to the discharge port.
The self-priming piston pump disclosed in Japanese Patent No. 3278982 includes a pump housing having a suction port, a discharge port, and an internal cavity; a first cylinder member having a cylinder bore and built into the internal cavity of the pump housing; a piston built into the cylinder bore of the first cylinder member to thereby form a pump chamber in the cylinder bore and adapted to change the volume of the pump chamber by means of axially reciprocating movement thereof; a suction valve provided in the piston, which opens when the volume of the pump chamber increases, and closes when the volume decreases; a discharge valve provided at the discharge side of the pump chamber, which opens when the volume of the pump chamber decreases, and closes when the volume increases; a second cylinder member disposed coaxially at the suction side of the first cylinder member and built into the internal cavity of the pump housing; and a sliding ring built into the cylinder bore of the second cylinder member to thereby dividingly form a suction chamber communicating with the suction port, and a discharge chamber communicating with the pump chamber or the suction chamber, and adapted to charge fluid into the discharge chamber from the suction chamber and into the pump chamber from the discharge chamber by means of axially reciprocating in relation to the piston and the second cylinder member and synchronously with a change in the volume of the pump chamber.
In the above-described conventional non-self-priming piston pump, the first cylinder member assumes the form of a sleeve having a fixed outside diameter and is press-fitted into the internal cavity of the pump housing to thereby maintain a seal between the same and the surface of the internal cavity. In the piston pump, in the course of press-fitting the first cylinder member into the internal cavity of the pump housing, a leading end portion of the first cylinder member may gall the surface of the internal cavity of the pump housing; as a result, the first cylinder member potentially fails to maintain a seal between the same and the surface of the internal cavity. Furthermore, press-fitting load may become excessively large and cause deformation (buckling) of the first cylinder member, potentially resulting in deformation of the cylinder bore, which accommodates the piston such that the piston can reciprocate axially therein.
In the above-described conventional self-priming piston pump, a spring case is crimped to the outer circumference of an end portion of the second cylinder member to thereby partially constitute a discharge valve, and covers the outer circumference of a portion of the first cylinder member, the outer circumference of the end portion of the second cylinder member, and the outer circumference of a washer sandwiched between the first cylinder member and the second cylinder member to thereby maintain a seal between the same and the outer surface of the first cylinder member. Also, a seal ring is attached to the outer circumference of each of the spring case and the second cylinder member. In this manner, various members are required to seal the first cylinder member and the second cylinder member.